To turn on Kiosk mode, the iPads must be supervised. Check out this help article to learn what supervision is all about and how you can enable it on your iOS devices,

This is how iOS devices are Supervised:

Once the iPads have been supervised, you can enroll with the device with Hexnode MDM and turn on Kiosk mode remotely.

Enroll devices with Hexnode MDM
Once your device is enrolled with Hexnode MDM, you can push configurations, set up restrictions, manage apps, enable Kiosk mode and more, all remotely.

Enable single app Kiosk mode
In Single app Kiosk mode, the iPad will be locked down to the selected app, users won’t be able to access other apps or device settings.

Enable Multi-app Kiosk mode
Multi-app Kiosk mode involves whitelisting apps which essentially locks down the iPad to the selected apps. The downside is that the Settings app will be available on the device by default. You won’t be able to deny access to it.